1. Field of the Invention
This invention relates to centrifugal pumps of the pitot tube type, and specifically relates to a modified inlet opening of a pitot tube for contacting and removing accumulated solids from the pump rotor.
2. Description of Related Art
Centrifugal pumps of the pitot tube type are well-known in the pumping industry as being useful in low flow/high pressure applications. Centrifugal pumps of the pitot tube type are generally structured with a closed rotor which is housed within the casing of the pump. A pitot tube assembly is positioned through a central opening of the rotor and is secured to the pump casing. A pitot tube arm of the pitot tube assembly is positioned within the rotor and is radially-oriented relative to the axis of the pump. The pitot tube arm is stationary while the rotor rotates about the pitot tube arm.
In operation, fluid enters into the rotor along the axis of rotation through radially-oriented fluid channels formed in the rotor cover. The fluid enters the internal space of the rotor where it picks up momentum and is subjected to centrifugal forces as the rotor spins. The fluid maintains its velocity at nearly the rotational speed of the rotor.
The pitot tube arm is structured with an inlet to receive fluid, and the inlet opening of the pitot tube is positioned near the inner periphery, or internal diameter, of the rotor. As the fluid is directed to the periphery of the rotor the fluid moves into the inlet of the pitot tube, through an inner channel of the pitot tube and out of the pump by way of a discharge outlet.
Traditionally, pitot tubes have been cast and machined with the inlet opening formed or configured as it will be used in the pump. However, after continued use of the pump, particularly when abrasive fluids are being processed by the pump, the impact of the fluid on the opening of the pitot tube causes degradation of the inlet and eventually pump efficiencies are adversely affected. The pitot tube arm must then be replaced in its entirety, which is very costly and increases operation costs.
The development of an insert for a pitot tube and the advantages of such inserts was first described in U.S. Pat. No. 5,997,243 to Shaw, issued Dec. 7, 1999 and assigned to the same assignee as the present application. U.S. Pat. No. 5,997,243 is incorporated herein by reference. The ""243 patent discloses a pitot tube inlet insert which allows the inlet opening of a pitot tube to be replaced after it has been degraded or damaged with use. The inlet insert eliminates the need to replace the entire pitot tube arm thereby reducing operating costs. The pitot tube insert described in the ""243 patent improves the efficiency of the pump and reduces or eliminates cavitation and degradation of the pitot tube inlet.
An additional problem occurs in pitot tube pumps which has not been previously addressed. That is, when the fluid being pumped contains particulate matter or solids, the impact of the fluid and solids on the pitot tube can be very damaging, with a resulting loss in head. Additionally, when solids are present in the fluid, the solids are thrown against the inside peripheral surface of the rotor under centrifugal force and can build up on the rotor. The accumulated solids built up on the interior peripheral surface of the rotating rotor then impact with the stationary pitot tube as the rotor spins and can cause an increase in drag on the rotor. Consequently, pump efficiency is sacrificed. The impact of the inlet against the solids further contributes to the degradation of the inlet and pitot tube arm.
Thus, it would be advantageous in the art to provide a pitot tube inlet which is designed to provide improved pump efficiencies when the pitot tube pump is used to process liquids containing solids that can build up on the rotor, and it would be advantageous to provide a pitot tube inlet insert which is designed to provide improved pump efficiencies under such conditions while also providing the advantage of being easily replaced at a relatively low cost.
In accordance with the present invention, a pitot tube inlet is configured to contact and remove the solids that build up on the inside peripheral surface of the rotor of a centrifugal pump to thereby improve the operational efficiency of the pump. While the present invention is principally described herein with respect to providing a pitot tube inlet insert that is configured for removing solids from the inside peripheral surface of the rotor, the design and configuration characteristics of the invention are equally applicable to a pitot tube which is unitarily cast in the traditional mode.
The pitot tube inlet of the present invention generally comprises an opening, which is positioned and sized to receive fluid from the peripheral portion of the rotor of a pitot tube pump, and a lip portion surrounding at least a part of the circumference or perimeter of the opening such that the lip portion is positioned to contact and remove solids that tend to accumulate and adhere to the inner peripheral surface of the rotor. The lip portion of the pitot tube inlet is generally directed away from the opening to provide a scoop-like portion which is capable of excising solids from the inner peripheral surface of the rotor.
The lip portion of the pitot tube inlet is also configured with a curved inner surface oriented about the opening of the inlet to direct solids into the opening of the pitot tube for discharge. The curvature of the inner surface not only facilitates directing the solids into the pitot tube, but increases the longevity of the pitot tube inlet by efficiently deflecting solids and liquid in a manner which decreases the usual degradation experienced in pitot tube inlets. The size, shape, dimension, angle, extension and/or circumferential extent of the lip portion may vary as long as the lip portion is capable of contacting and removing accumulated solids from the inner peripheral surface of the rotor to reduce or eliminate drag on the rotor to improve the operational efficiency of the pump.